Evaluation location: Iowa, United States
Two hundred fifty-nine accessions were tested for resistance to Stewart's wilt caused by Pantoea (Erwinia) stewartii. Plots were planted on 28-May-2010 at Ames, IA. Three replications of single-row plots were planted per entry. Inoculations were done by the pinprick method on 06-JUL at the 7 to 9-leaf stage and on 13-JUL at the 10 to 11-leaf stage. Inoculum was produced from a mixture of three isolates, ES9211, ES9239 and ES9245 (Iowa origin). Disease ratings were done from 18-AUG to 02-SEP. Ten to 12 plants were rated per plot and an average rating was calculated for each plot. Disease reactions were scored on a 1-9 scale where: 1= no appreciable spread of symptoms from pinpricks (less than 1 cm); 2= limited spread of lesions from pinpricks (1 to 3 cm); 3= limited spread from pinpricks with water-soaking, chlorosis, or necrosis; lesions spreading mainly toward tips of leaves; 4= abundant spread of lesions in both directions on inoculated leaves, with water-soaking, chlorosis, or necrosis, but no evidence of systemic infection; 5= lesions spread to the leaf base, reaching the stalk; minimal systemic infection observed; 6= moderate systemic infection with 5-25% symptomatic leaf area on non-inoculated leaves; 7= abundant systemic infection and stunting with 25-50% of the leaf area affected; 8= severe systemic infection and stunting with 50-90% of the plant infected; 9= 90-100% infection, severe necrosis or dead. Accessions with 1, 2 (highly resistant) and 3 (resistant) ratings have definite resistance. Accessions with a 4,5,6 ratings are moderately susceptible and accessions with 7,8,9 ratings are highly susceptible. Six inbreds were used as checks, Mo21R (resist.) which had an average rating of 1.0, B37 Ht (mod. res.), with an average rating of 3.1, A629 (mid-check) with an average rating of 4.1, A632 Ht (mod. susc.) with an average rating of 6.4, Mt42 (very susc.) with an average rating of 8.9 and C42 (highly susc.) with an average rating of 9.0.